Method for regulating the pretreating and esterifying of cellulose



Patented Dec. 8, 1936' UNITED STATES PATENT OFFICE METHOD FOR REGULATING THE PRE- TREATING AND ESTERIFYING OF CEL- LULOSE poration of New Jersey No Drawing. Application'July 25, 1934, Serial No. 736,966

3 Claims.

This invention relates to the regulation of the steps, in the preparation of cellulose esters, of pretreating and esterifying the cellulose by determining the content of water or of fatty acid anhydride present in these respective steps and adjusting the conditions thereof in accordance with this determination.

Heretofore in processes for the fibrous esterification of cellulose it has as a rule been the practice in determining the progress of the esterification to remove a sample of the fibers, and after a thorough washing with water either to analyze the fibers for combined acyl or to test their solubility in certain organic solvents. Analysis of a sample of the fiber is a slow and tedious procedure so that when the results thereof become known the acetylation has advanced greatly. Therefore those results are of little value when they are finally obtained. The testing of the sample with solvents is not very satisfactory as there are other factors than acetyl content which influence solubility. Also the fact that an ester is soluble in a certain solvent does not as' a rule disclose the precise percentage of combined acyl therein but rather only within What rather broad range the percentage of combined acyl is found.

In processes for the pretreatment of cellulose wherein it was desired that the mass be anhydrous, such as that described in Malm application Serial No. 526,121 filed March 28, 1931, the practice previously has been, knowing the percentage of moisture in the cotton and the reagents employed, to calculate the amount of acetic anhydride which would combine with the water present and add that amount ora small excess to the pretreatment bath.

In order to be able to reproduce an esterification process and obtain a product with desired properties, it is necessary to reproduce pretreattreatment of the cellulose is determined by the following factors:

1. Temperature 2. Time 3. Amount of catalyst present 4. Amount of water present Factors 1, 2 and 3, obviously, can be very easily controlled but the control of the water content of the pretreatment bath has been very difiicult due to the fluctuations in the water content of the organic acid and particularly of the cotton in the pretreatment or esterification of cellulose 10 a may be determined and by means of that knowledge the treatment of the cellulose may be intelligibly controlled. Other objects will appear herein.

We have now found a method by which the 15 water content of a pretreatment mass may be accurately and quickly determined while in the meantime the action of the pretreatment bath on the cellulose is arrested by keeping the temperature down. Then from the findings of the 20 amount of water present, the composition of the bath may be adjusted as desired. As a rule it is desired that there be no water nor organic acid anhydride present. As the water content is accurately determined by our method, an amount of anhydride which will combine quantitatively with that water may be added so that there is neither Water nor anhydride present in the bath when the pretreatment occurs.

In practice the cellulose, preferably cotton, 30,

drawn and the water content determined. This may be accomplished by adding a measured quantity such as'about 1 gm. of the pretreatment liquid to 10 c. c. of a standardized solution of acetic anhydride in glacial acetic acid to which some (a known amount of) perchloric or sul- 40 furic acid has been added. The Whole may be permitted to stand for 15-20 minutes at room temperature or above, whereupon 10 c. c. of a 0.2 M solution of aniline in acetic acid is then added. The excess of aniline over that which combines with the acetic anhydride is determined by titration with a standardized solution of perchloric acid, sulfuric acid, sulfoacetic acid or the like, allowance being made for the mineral acid which was already present in the mix- 50.

catalyst.

out in the usual manner.

ture. Various indicators such as" crystal violet, methyl violet, para rosaniline, alpha-safranine, a freshly prepared solution of benzoyl auramin, naphtholbenzein or even xylene cyanol may be employed. As is apparent to those skilled in the art, the calculations which are based on the fol-' lowing equations are very simple:

or other aromatic amines such as dichloroaniline, alpha naphthylamine, di-naphthylamine, the toluidines or the xylidines might be employed. Secondary amines might also be employed in the present invention.

It is desirable that all the solutions employed be prepared in glacial acetic acid as the solvent although of course other solvents particularly formic, propionic or butyric acidsmight be employed instead. Also non-hyd'rolytic solvents such as ethylene chloride can be mixed with the acetic acid if desired. When formic acid is used it is necessary to dilute with acetic acid however, before the final titration.

After the amount of water which is present in the pretreatment mixture has been determined, the proper amount of organic acid anhydride, such as acetic, or water to bring the water content of the bath to the desired point may be added. Thus if a completely anhydrous bath is desired an amount of organic acid anhydride such as acetic just sufficient to combine with the water present will be added. If a pretreatment bath containing a certain percentage of water is desired, water will be added if that percentage is more than that of the water already present. If the percentage of water already present is greater than that desired obviously an amount of anhydride calculated to combine with the amount of water over that desired will be added. In this preliminary treatment the water and anhydride combine rapidly so that :there should be no reaction upon the cellulose by the anhydride clue to its reacting at once with the water to form acetic acid. Also acetic anhydride does not readily acetylate cotton below 50 F. with the ordinary concentration of When the anhydride and water have combined, such as in about 15 minutes the temperature of the mixture may be raised to the desired pretreatment temperature such as 100' F. and the pretreatment may be carried Thus regardless of the variation of the moisture content from time to time of the cellulose and the organic acids employed, a very uniform, readily reproducible pretreatment is made possible by the present invention.

The following example illustrates a pretreatment carried out in accordance with the present invention:

500 gms. of cotton linters is placed in a mixture consisting of 4000 gms. of glacial acetic acid and 10 gms. of HzSOi (95%) at a temperature of approximately 15 C. After thorough mixing, a 1 gm. sample of the bath is placed in 10 c. c. of a solution of 51 gms. of acetic anhydride in a liter of a mixture of acetic acid and .5 gm. of sulfuric acid and allowed to stand 15-20 minutes at room temperature (about 20 C.) 10 c. c. of a 0.2 M aniline solution in acetic acid is added thereto, to combine with the excess of acetic anhydride present. The excess aniline is then determined by titrating with a 0.1 N soluof perchloric acid in water. Say for instance that 3 c. c. of the .l N perchloric acid was re quired. This indicates an aniline content of .028 gm. in the sample. There was also .007 gm. of sulfuric acid present in the sample whichrequires .0066 gm. of aniline to combine therewith. Thus .0346 gm. of the aniline is accounted for. As the 10 c. c. of aniline solution added contained .223 gm. aniline, the amount of aniline which combined with the anhydride present was .1884 gm. The amount of anhydride necessary to combine with this amount of aniline was slightly less than .21 gm. As .51 gm. of acetic anhydride was employed originally the amount of acetic anhydride used up in combining with the Water of the 1 gm. sample was .3 gm. showing the water content of the 1 gm. sample to be .053 gm. As the liquids comprising the bath weigh 4510 gms. the content of water therein amounts to 239 gms.

If an anhydrous pretreatment bath is. desired the addition of slightly more than 1354 gms. of acetic anhydride is necessary. Of course if 85% acetic anhydride is employed, the amount to be added should be such that it will supply slightly more than 1354 gms. of actual (CI-I300) 2O thereto. The temperature of the mixture may then be increased to 80-90 F. and'maintainedat that point for several hours, preferably 2-4, althrough 2 hours is usually sumcient.

As pointed out previously this' method' is also adapted to determine the progress of the fibrous esterification of cellulose. In dope methods of esterifying cellulose, the progress of the esterification may be followed by the appearance of the fibers, esterification being near completion when the fibers are completely disintegrated or dissolved by the esterification bath. In fibrous methods of esterifying cellulose the fibers retain the same appearance throughout the entire esterification so that some other method of determining the progress of the esterification than that employed for dope processes is obviously neces sary. Heretofore the progress of the fibrous esterification of cellulose has usually been followed by removing samples of the cellulose fibers, washing them thoroughly and either determining their combined acyl content or testing their solubility in various organic solvents. This method is far from being satisfactory due to the time necessary to arrive at the finalresult and the difiiculty of obtaining representative samples of the fibers.

By our method the progressof the esterification can be followed very accurately by determining the amount of unused anhydrideipresentin the esterication mixture. thefollowing manner:

A known quantity of an amine, such as aniline, is added to a measured sample of the esterificatlon mixture. The organic acid anhydride reacts with the aniline and the unused aniline can'be determined by titration with an anhydrous solution of a mineral'a'cid. The amount of anhydride can then be calculated as explained above. correction beingmade for'the amount of the catalyst in the mixture. sample may be determined by means of an acetic acid solution of sodium acetate. For example.

during a fibrous esterificationprocess samples of the liquid were removed at intervals and the anhydride content of the bath was determined This maybe done in The amount of catalyst present ina.

therefrom. The data below shows the ease with which the esterification may be followed:

Time (hrs) Percent acetic anhydride The 12 hour sample indicates that the esterification is substantially completed at that point. It is apparent that if the amount of cellulose and acetic anhydride employed originally are known, the anhydride concentration at which cellulose will be fully esterified may be calculated. When this point is reached the reaction is finished and the fibers may be removed from the esterification mixture at this time thus saving time over a process in which the progress of the reaction is not determined.

The present invention is not restricted to the preparation of cellulose acetates as other esters such as contain propionyl or butyryl groups might be prepared by employing the corresponding acids or anhydrides with the present invention employed for regulating the reaction. For instance cellulose may be esterified in a bath containing acetic and butyric acids and acetic anhydride in which the pretreatment might be either with acetic acid or a mixture of acetic and butyric acids (in each case with or without catalyst) and in which it would be desirable to know the water content of the pretreatment, so that it may be adjusted as desired. Instead of the butyric acid, propionic acid might be used to form a cellulose acetate propionate. Or a cellulose acetate proprionate might be prepared by reacting upon cellulose with a bath containing acetic acid and proprionic anhydride. In that case it might be desired to pretreat the cellulose with the acetic acid (with or without catalyst). In such a case the water content of the pretreatment bath might be determined by the present invention so that a pretreatment of a known composition might be used.

Also processes of this nature might be carried out using a non-solvent in the esterification bath so that the cellulose ester is produced in fibrous form. In that case as explained above the progress of the esterification may be determined by the present invention. Obviously if some other anhydride than acetic is employed that fact should be taken into account in the calculations.

What we claim as new and desire to secure by Letters Patent of the United States is:

1. A method for determining the value from which the water and organic acid anhydride content of a bath employed in the preparation of cellulose esters may be calculated, which comprises withdrawing a measured sample of the bath, assuring the presence of uncombined organic acid anhydride in the sample, supplied by adding a measured amount of acetic anhydride to the sample, adding to the sample a measured amount of an anhydrous standard solution of aniline in a lower fatty acid to combine with the organic acid anhydride present in the sample and then titrating this anhydrous solution containing aniline dissolved in a lower fatty acid with a standardized solution of mineral acid and determining the amount of standardized mineral acid which was employed.

2. A method for determining the value from which the organic acid anhydride content of a bath employed in the preparation of cellulose esters may be calculated which comprises adding to a measured sample of the bath containing uncombined organic acid anhydride a measured amount of an anhydrous standard solution of aniline in acetic acid to combine with the anhydride present and then titrating this anhydrous solution containing aniline dissolved in acetic acid with a standardized solution of a mineral acid.

3. A method for determining the value from which the water content of a bath employed in the preparation of cellulose esters may be calculated which comprises adding a measured quantity of the bath to a measured amount of a standardized solution of acetic anhydride in anhydrous acetic acid which contains a small amount of catalyst to promote the combination of the acetic anhydride with any water which may be present, adding thereto a measured amount of an anhydrous standard solution of aniline in acetic acid to combine with the anhydride in excess of that which combined with the water present and then titrating this anhydrous solution containing aniline dissolved in acetic acid with a standardized solution of a mineral acid.

CARL J. MALM. GALE F. NADEAU. 

